http://www.daviscup.com/ when there's a match in progress you can click on the live score....all points as they happen and graphical details about were the ball went, who's serving, how fast and what's happening on court

http://www.livescore.com/tennis.dll all results from the day, also has live scoring during the matches - shows all matches happening in the world, not only the biggies (aka masters and davis cup)